1. Field of the Invention
The present invention relates generally to a liquid crystal display device, and more particularly to a liquid crystal display device which is configured to have a pixel electrode and a counter-electrode on one of substrates that constitute a liquid crystal display panel.
2. Description of the Related Art
In recent years, flat-panel display devices, which take the place of CRT displays, have vigorously been developed, and liquid crystal display devices, above all, have attracted attention because of advantages of light weight, small thickness and low power consumption. In particular, in an active matrix liquid crystal display device in which a switching element is provided in each of pixels, attention has been paid to the structure which makes use of a transverse electric field (including a fringe electric field) of an IPS (In-Plane Switching) mode or an FFS (Fringe Field Switching) mode.
The liquid crystal display device of the IPS mode or FFS mode includes a pixel electrode and a counter-electrode which are formed on an array substrate, and liquid crystal molecules are switched by a transverse electric field that is produced between the pixel electrode and the counter-electrode and is substantially parallel to the major surface of the array substrate. In addition, polarizer plates, which are disposed such that their axes of polarization intersect at right angles, are disposed on the outer surfaces of the array substrate and the counter-substrate. By this disposition of the polarizer plates, a black screen is displayed, for example, at a time of non-application of voltage. With the application of a voltage corresponding to a video signal to the pixel electrode, the light transmittance (modulation ratio) gradually increases and a white screen is displayed.
In this liquid crystal display device, if the counter-substrate is charged with, e.g. static electricity, a vertical electric field is produced between the counter-substrate and the array substrate. If the vertical electric field is produced, an alignment defect of liquid crystal molecules occurs, leading to degradation in display quality. In order to prevent charging of the counter-substrate, there has been disclosed a technique in which a shield electrode is disposed on the outer surface or inner surface of the counter-substrate (see Jpn. Pat. Appln. KOKAI Publication No. 2005-234547).
In the IPS more or FFS mode liquid crystal display device, the thickness of the liquid crystal layer is relatively small. Thus, in the case where the shield electrode is disposed on the inner surface of the counter-substrate, the shield electrode is positioned close to the counter-electrode and pixel electrode. Consequently, a vertical electric field, which occurs between the shield electrode, on the one hand, and the counter-electrode and pixel electrode, on the other hand, may cause an alignment defect of liquid crystal molecules and degradation in display quality.
On the other hand, as regards the structure in which the shield electrode is disposed on the outer surface of the counter-substrate, in the case where the shield electrode is formed in a solid fashion on the outer surface of a mother-substrate which becomes the counter-substrate, a part of the shield electrode may possibly peeled off when the counter-substrate of a predetermined size is cut out of the mother-substrate, and the peeled matter may become minute electrically conductive foreign matter and contaminate the surrounding.
For example, if a mounting section for connecting wiring on the array substrate and a signal supply source such as a driving IC is contaminated, a problem, such as short-circuit between terminals, may occur. This may cause degradation in display quality and reliability of the liquid crystal display device, and a decrease in manufacturing yield.
Moreover, in the structure in which a liquid crystal material is vacuum-injected, if the area of an injection port is contaminated, electrically conductive foreign matter would be drawn and mixed in the liquid crystal layer at the time of injecting the liquid crystal material. Such electrically conductive foreign matter may become a factor which causes short-circuit between wiring lines or electrodes, and an alignment defect of liquid crystal molecules. Hence, the display quality of the liquid crystal display device may be degraded, and the manufacturing yield may be lowered.